# Can i do this in ruby? a simulation process **URL:** \ **Category:** Ruby\ **Created:** [August 17, 2010, 11:11am UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412 "2010-08-17T11:11:00Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 11:11am UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/1 "2010-08-17T11:11:00Z")
still i don’t know how to begin my program on this problem: A superhighway connects one large metropolitan area to another. A vehicle leaves the first city every 5-35sec. 20% of the vehicles have 1 passenger, 30% have 2 passengers, 10% have 3 passengers and and 10% have 4 passengers. the remaining 30% of the vehicles are buses, which carry 40 people. It takes 50sec-1min &10sec for vehicles to travel between the two metropolitan areas. How long does it take for 500 people to arrive in the second city. Requirements: 1. A simulation process of the movement of vehicles from one point to another. 2. The time (in minutes) for 500 people to arrive in the second city. i can’t even think on how can i start this one in ruby a newbie like me have only limited knowledge on ruby. can someone help with my program? ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 11:40am UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/2 "2010-08-17T11:40:31Z")
> Requirements: > > 1. A simulation process of the movement of vehicles from one point to > another. > 2. The time (in minutes) for 500 people to arrive in the second city. > > i can’t even think on how can i start this one in ruby a newbie like me > have only limited knowledge on ruby. can someone help with my program? You sure can do it in ruby but first you have to decide what ruby have to do for you: take a sheet of paper and write down the differents steps each Vehicle has to go throught in order to reach the second city. I’m sure you will see more clearly what you have to do next to implement each step. Hint: it have to do with probability distributions and you will most certainly need the metho ‘rand’ Cheers, ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 11:52am UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/3 "2010-08-17T11:52:16Z")
Jean-Julien F. wrote: > > Requirements: > > > > 1. A simulation process of the movement of vehicles from one point to > > another. > > 2. The time (in minutes) for 500 people to arrive in the second city. > > > > i can’t even think on how can i start this one in ruby a newbie like me > > have only limited knowledge on ruby. can someone help with my program? > > You sure can do it in ruby but first you have to decide what ruby have > to do for you: take a sheet of paper and write down the differents > steps each Vehicle has to go throught in order to reach the second > city. I’m sure you will see more clearly what you have to do next to > implement each step. > > Hint: it have to do with probability distributions and you will most > certainly need the metho ‘rand’ > > Cheers, Cheers Thanks, anyway i already did writing and other stuff but the only problem is that i don’t know to start my code. ☹ ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 12:01pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/4 "2010-08-17T12:01:01Z")
> Cheers Thanks, anyway i already did writing and other stuff but the only > problem is that i don’t know to start my code. ☹ Try to create a Vehicle class where you compute the arrival time and the number of passengers based on a departure time. Then make a loop of say 500 vehicles (to be sure everybody arrive at the end) and create a list of vehicles that are launched every 5-35s. Do not forget to sort the list based on arrival time rather than departure time. In the end, it should give you something like […] 442 passengers where there after 654 seconds 444 passengers where there after 691 seconds 448 passengers where there after 717 seconds 449 passengers where there after 746 seconds 489 passengers where there after 761 seconds 529 passengers where there after 790 seconds Cheers, ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 12:32pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/5 "2010-08-17T12:32:03Z")
Bruce W. wrote: > i can’t even think on how can i start this one in ruby a newbie like me > have only limited knowledge on ruby. can someone help with my program? To start with, I’d ask the following: how would you perform the simulation manually, for example using a pencil, some pieces of paper, and some dice? (You can use any imaginary dice you need, e.g. a 30-sided die or a 20-sided die). I strongly suggest you do it for real, for a number of vehicles. When you see the individual steps that you’re doing, you’ll have a clearer idea of the individual steps your program needs. Then you can come back and ask more specific questions. ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 1:36pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/6 "2010-08-17T13:36:26Z")
Hmm, I may or may not disagree with you on what the output should be. I can’t speak for his assignment, but in real life, I would think it would be more useful to perform the simulation some number of times, printing out the number of seconds it took to get to 500 passengers each time, and the average of all the trials. It’s not clear to me from the description of the assignment whether the requirement is for the results of a single trial (rather silly) or an average. Anyway, I did this, for fun, and consistently got an average of around 833 seconds on average for 100000 trials. Anyone else give this a shot? I’m curious to see whether different implementations give different results. The standard deviation seems to be pretty high. On Tue, Aug 17, 2010 at 6:00 AM, Jean-Julien F. \< ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 2:25pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/7 "2010-08-17T14:25:00Z")
Andrew W. wrote: > Anyway, I did this, for fun, and consistently got an average of around > 833 > seconds on average for 100000 trials. Anyone else give this a shot? I’m > curious to see whether different implementations give different results. Ruby quiz 🙂 After 10,000 trials I got an average of 803 seconds, and after a second 10,000 trials I got 807 seconds. But I don’t think we should post any code until the OP has had a go. I would certainly expect wide variation between runs, since it would be affected very strongly by when the buses set off. However I think the point of the exercise is really the simulation, because it becomes very simple if you treat it statistically. (1) Average number of occupants per vehicle = 0.2_1+0.3_2+0.1_3+0.1_4+0.3\*40 = 13.5 (2) You can ignore the different travel times. The average rate at which vehicles depart must be the same as the average rate at which they arrive (law of conservation of vehicles) (3) The vehicles depart on average every 20 seconds So you should get an average of 0.675 passengers per second, which implies 500 passengers will pass any particular point after 740.7 seconds. It then takes each passenger an average of 60 seconds to get from A to B, so that makes 800.7 seconds for the original question. I would expect the real simulation answer to be slightly different because of the discontinuous (bursty) nature of arrivals. ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 2:47pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/8 "2010-08-17T14:47:52Z")
> After 10,000 trials I got an average of 803 seconds, and after a second > 10,000 trials I got 807 seconds. But I don’t think we should post any > code until the OP has had a go. Interesting. Sounds like I’ve got a bug to hunt down. Agreed, as far as posting code. > (3) The vehicles depart on average every 20 seconds > > So you should get an average of 0.675 passengers per second, which > implies 500 passengers will pass any particular point after 740.7 > seconds. > > It then takes each passenger an average of 60 seconds to get from A to > B, so that makes 800.7 seconds for the original question. Nice analysis. I did a very similar set of calculations, and came up with roughly the same result. > I would expect the real simulation answer to be slightly different > because of the discontinuous (bursty) nature of arrivals. Can you expand on this? I’m curious what you mean, from a mathematical perspective. ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 2:46pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/9 "2010-08-17T14:46:42Z")
2010/8/17 Andrew W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > Hmm, I may or may not disagree with you on what the output should be. I > can’t speak for his assignment, It was just to get him the idea. > Anyway, I did this, for fun, and consistently got an average of around 833 > seconds on average for 100000 trials. Anyone else give this a shot? I’m > curious to see whether different implementations give different results. The > standard deviation seems to be pretty high. I also did, twice on 100000 trials: First: In mean, it took 808.3 seconds to go there. Second: In mean, it took 809.3 seconds to go there. It’s quite consistent with the little calculation Brian explained. I would expect the mean result to always be above the 800.7 seconds Brian found as there is very little chance that the sum of the passengers arriving in town be exactly 500 (it ranges from 500 to 539 due to the buses) Cheers, ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 2:56pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/10 "2010-08-17T14:56:39Z")
> It’s quite consistent with the little calculation Brian explained. > I would expect the mean result to always be above the 800.7 seconds > Brian found as there is very little chance that the sum of the > passengers arriving in town be exactly 500 (it ranges from 500 to 539 > due to the buses) Ah yes, I see now what Brian meant by “bursty”. Thanks for the results! ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:19pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/11 "2010-08-17T15:19:06Z")
A superhighway connects one large metropolitan area to another. A vehicle leaves the first city every 5-35sec. 20% of the vehicles have 1 passenger, 30% have 2 passengers, 10% have 3 passengers and and 10% have 4 passengers. the remaining 30% of the vehicles are buses, which carry 40 people. It takes 50sec-1min &10sec for vehicles to travel between the two metropolitan areas. How long does it take for 500 people to arrive in the second city. 20% of vehicles (1passenger) -\> must transfer 100(20% of 500) people from A -\> B 30% of vehicles (2passenger) -\> must transfer 150 people from A -\> B 10% of vehicles (3passenger) -\> must transfer 50 people from A -\> B 10% of vehicles (4passenger) -\> must transfer 50 people from A -\> B 30% of vehicles(bus) (3passenger) -\> must transfer 150 people from A -\> B 5-35sec (rand?) -\> departure time for vehicles from A to B + 50sec - 1min & 10sec ( 70sec? im a ryt? rand?) -\> traveling time from A -\> B and then 50sec - 1min & 10sec ( 70sec? im a ryt? rand?) -\> traveling time from B -\> A 5-35sec (rand?) -\> departure time for vehicles from B -\> A i would like to if you used rand() in departure time/traveling time… ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:19pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/12 "2010-08-17T15:19:34Z")
A superhighway connects one large metropolitan area to another. A vehicle leaves the first city every 5-35sec. 20% of the vehicles have 1 passenger, 30% have 2 passengers, 10% have 3 passengers and and 10% have 4 passengers. the remaining 30% of the vehicles are buses, which carry 40 people. It takes 50sec-1min &10sec for vehicles to travel between the two metropolitan areas. How long does it take for 500 people to arrive in the second city. 20% of vehicles (1passenger) -\> must transfer 100(20% of 500) people from A -\> B 30% of vehicles (2passenger) -\> must transfer 150 people from A -\> B 10% of vehicles (3passenger) -\> must transfer 50 people from A -\> B 10% of vehicles (4passenger) -\> must transfer 50 people from A -\> B 30% of vehicles(bus) (3passenger) -\> must transfer 150 people from A -\> B 5-35sec (rand?) -\> departure time for vehicles from A to B + 50sec - 1min & 10sec ( 70sec? im a ryt? rand?) -\> traveling time from A -\> B and then 50sec - 1min & 10sec ( 70sec? im a ryt? rand?) -\> traveling time from B -\> A 5-35sec (rand?) -\> departure time for vehicles from B -\> A i would like to know if you used rand() in departure time/traveling time… Cheers ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:28pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/13 "2010-08-17T15:28:17Z")
> i would like to know if you used rand() in departure time/traveling > time… I used rand() for both departure time and traveling time, assuming all the times were equally likely. You bring up an interesting point about going from B -\> A. In my simulation, I only considered vehicles going in one direction. Seems like the specification is unclear about whether they are leaving every 5-35 seconds from both cities or just one. Though if they’re going from both directions, there’s certainly no guarantee that you will ever move a total of 500 from one to the other. ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:22pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/14 "2010-08-17T15:22:03Z")
sorry for the double post 🙂 ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:29pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/15 "2010-08-17T15:29:32Z")
Bruce W. wrote: > i would like to know if you used rand() in departure time/traveling > time… Yes. rand() by itself gives a random number between 0.0 and 1.0 (well actually 0.99999999…). Hence, rand\*30.0 gives you a value between 0 and 30. ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:31pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/16 "2010-08-17T15:31:13Z")
Hello Bruce, > 50sec - 1min & 10sec ( 70sec? im a ryt? rand?) -\> traveling time from B > -\> A > 5-35sec (rand?) -\> departure time for vehicles from B -\> A > > i would like to know if you used rand() in departure time/traveling > time… Yes, we did. But also when taking into account the number of passengers: in real life, on a certain amount of time, you don’t know if there will be a tad more buses and a tad less monodrivers than in mean. The only thing you do know is that if you count for a very long time, you end up with the given percentages. Cheers, ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:35pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/17 "2010-08-17T15:35:55Z")
Ah. Yes, I didn’t mean to say that I used rand without any parameters. I used the fact that, for example, to get a random number from 0 to 5, inclusive, you can call rand(6). ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:36pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/18 "2010-08-17T15:36:07Z")
Bruce W. wrote: > 20% of vehicles (1passenger) -\> must transfer 100(20% of 500) people > from A -\> B No, and in any case that’s the wrong approach for a simulation. In any particular run, it’s possible (although rather unlikely) that all the vehicles will depart will all be buses. Or that they will all be cars with one driver. In practice, the mix will vary between runs, and you don’t know in advance what it will be. Treat each vehicle individually. Each one has its own departure time, its own arrival time, and its own number of occupants. If you do the simulation by hand, you’ll see what I mean. To start with, you could use ruby as the random number generator, while you do the rest of the work by hand. Suppose the first vehicle leaves on the dot of 12:00:00 (or 0 seconds past midday). How many passengers does it contain? When does it arrive? When does the second vehicle leave? And so on. ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:39pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/19 "2010-08-17T15:39:26Z")
Yes, but you take that into account by doing a large number of trials, right? You still consider all values equally likely in any individual case? On Tue, Aug 17, 2010 at 9:29 AM, Jean-Julien F. \< ---
**Author:** ![midnightcoder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@midnightcoder](https://www.ruby-forum.com/u/midnightcoder)\ **Post date:** [August 17, 2010, 3:34pm UTC](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412/20 "2010-08-17T15:34:09Z")
> You bring up an interesting point about going > from B -\> A. In my simulation, I only considered vehicles going in one > direction. Seems like the specification is unclear about whether they are > leaving every 5-35 seconds from both cities or just one. Specifications are clear, at least to me: “A vehicle leaves the first city every 5-35sec. […] How long does it take for 500 people to arrive in the second city.” > Though if they’re > going from both directions, there’s certainly no guarantee that you will > ever move a total of 500 from one to the other. Then the problem is turning into a (sort of) random walk: it’s getting far more complicated (but far more interesting ?) Cheers, [Next page](https://www.ruby-forum.com/t/can-i-do-this-in-ruby-a-simulation-process/193412.md?page=2)